The 2nd son's son and a's daughter's son are just creating false claim. Absolutely no worries.
As per your statement, the revenue records are bearing your father's name from 1972 and your name from 1995.
you are in possession of the property.
As per law, any transaction done 30 years before are deemed to be valid. in your case, your father is the owner as per sale deed, revenue records and has been the owner since 1972 and thereafter you are the owner of the property.
Moreover in your case, legally, the 2nd son of A and A's Daughter should have contested the title between 1961 to 1965(3year limitation) or if they were minor till 1972, they should filed a case within 3 years of they becoming major.
in your case, it is A's 2nd son's son and A's daughter's son who are now filing a suit. the suit will fail on account of the following points :
a) Law of limitation.
b) What the father(2nd son)/Mother(a's daughter) failed to do, their children cannot do (filing of suit against first son and your father way back in 1972 or 3 years after they(2nd son and A's daughter) became major.
c) You are the owner by virtue of a sale deed and all records are mutated in your name. You are in possession of the property for 43 years. even assuming you have no title, since you are in possession of the property for 43 years, as per law, you are in adverse possession.
Hence you can be rest assured of your title and ownership.